If a wellbore tool is positioned down hole in advance of its required operation, the tool must be actuated remotely. Indexing mechanisms may be useful where a tool is intended to be actuated through a number of positions.
For example, in some tools, indexing mechanisms are employed to actuate a tool through a number of inactive positions before it reaches an active position. For example, indexing mechanisms may be employed in wellbore tools for wellbore fluid treatment such as staged well treatment. In staged well treatment, a wellbore treatment string is deployed to create a plurality of isolated zones within a well and includes a plurality of openable ports that allow selected access to each such isolated zone. The treatment string is based on a tubing string and carries a plurality of packers that can be set in the hole to create isolated zones therebetween about the annulus of the tubing string. Between at least selected packers, there are openable ports through the tubing string. The ports are selectively openable and include a sleeve thereover with a sealable seat formed in the inner diameter of the sleeve. By launching a ball, the ball can seal against the seat and pressure can be increased behind the ball to drive the sleeve through the tubing string to open the port in one zone. The seat in each sleeve can be formed to accept a ball of a selected diameter but to allow balls of lower diameters to pass.
Unfortunately, due to size limitations with respect to the inner diameter of wellbore tubulars (i.e. due to the inner diameter of the well), such wellbore treatment systems may tend to be limited in the number of zones that may be accessed. For example, if the well diameter dictates that the largest sleeve in a well can at most accept a 3¾ ball, then the well treatment string will generally be limited to approximately eleven sleeves and, therefore, can treat in only eleven stages.